As scientists continue grappling with efforts to make solar power more efficient, some researchers are turning to the original solar cells — the ones in plants. Plants use photosynthesis to generate the energetic compounds needed to sustain life. Researchers have found that some of these photosynthetic compounds can be used to generate energy outside of plants, and a new experiment at Vanderbilt University has succeeded in making these hybrid solar cells more efficient.

The work centers around a protein called Photosystem I, or PS1. This is an important compound in the membranes of chloroplasts, the energy producing structures in plants. PS1 has a large role in absorbing light in order to drive the production of electrons on one side of the Chloroplast membrane. This is of biochemical interest in plants, but the production of electrons can also be harnessed to produce electric charges in so-called biohybrid solar cells.

The appeal is that PS1 can operate at nearly 100% efficiency, whereas regular photovoltaic cells are sitting at around 40%. The challenge has been to maintain that efficiency when producing solar cells with PS1 proteins. In the new Vanderbilt study, a purification of spinach PS1 protein was applied to a silicon wafer that had been treated in such a way that it had a positive charge. This turned out to be the key.

PS1 in plant cells is embedded in a membrane, so all these PS1 structures are facing the same way. If PS1 is applied to a surface and dried, it ends up pointing in all different ways. That’s bad for energy production. The positively charged silicon surface helps align more of the proteins so the resulting biohybrid cell outputs more power.

The Vanderbilt cells produce about 850 microamps of current per square centimeter. That’s still far below what regular photovoltaics can do, but it’s a 2.5x improvement over past biohybrid cells. Additional challenges in longevity are being investigated, but biohybrid cells still have a way to go.